We did a similar trip in June, omitting Deadwood, Wounded Knee museum and Devils Tower (been there before) but adding Mt Rushmore, Wind Cave, Needles Highway and the 1880s train. You will have plenty of time to see all that in 8-10 days. I agree with wing_zealot that Wall Drug is 2-3 hours tops...The Badlands and the museum will add 3 hours too so it would be a day trip at the most. Before my trip, some had suggested we stay near Wall overnight and hit those attractions (Wall, Badlands) but we stayed in Custer the entire time and the drive from Custer wasn't bad.